The present invention relates to a light-sensitive composition for forming a black matrix which is used as a means for shading in a liquid crystal display device, a black matrix produced from the composition and a color filter substrate carrying such a black matrix as well as a liquid crystal display device in which the foregoing black matrix is incorporated.
The liquid crystal color display device comprises a color filter substrate which comprises a glass substrate and red (R), green (G) and blue (B) picture elements regularly arranged on the substrate and thus can display color images thereon. In general, the color filter further comprises a shade pattern called black matrix which is arranged such that it fills up the spaces formed between picture elements to thus improve the contrast ratio of displayed images to the background.
The black matrix is formed from a material such as a metal or metal oxide film or a resin film comprising a pigment and the patterning thereof is carried out by the photolithography technique. For instance, Japanese Un-examined Patent Publication (hereunder referred to as "J.P. KOKAI") No. Sho 63-309916 discloses a method for forming a black matrix comprising applying a light-sensitive resin solution containing a pigment dispersed therein onto a transparent substrate, exposing the coated layer to light rays and then developing the exposed light-sensitive resin layer.
In addition, J.P. KOKAI No. Hei 1-152449 discloses a method for forming a black matrix and picture elements of a color filter on a single substrate. More specifically, the method comprises the steps of first applying, onto the surface of a glass substrate, a pigment dispersion comprising a photopolymerizable light-sensitive composition and carbon black, exposing to light and developing the exposed coated layer to form a black matrix pattern and then repeating procedures for patterning the surface of a coated layer similar to those used above to form a color filter comprising R, G and B picture elements in such a manner that these picture elements and the openings of the black matrix overlap one another.
However, the black matrix of the resin film containing the pigment suffers from a problem in that the liquid crystal display device is incompletely operated due to a decrease in the specific resistance of a liquid crystal and corresponding insufficient charge-retention of the liquid crystal layer (or molecules), as compared with the black matrix formed from a metal oxide film such as chromium oxide film.
J.P. KOKAI No. Hei 2-166422 discloses a liquid crystal display device comprising a plurality of transparent picture element-electrodes formed on a transparent substrate and a black matrix formed thereon so as to fill up the spaces remaining between the picture element-electrodes. In this system, the color filter and the black matrix are separately formed on two discrete substrates opposed to one another. The black matrix is arranged on the surface of driving electrodes while coming in contact therewith and therefore, there is not observed any aberration of the position of the black matrix relative to those of the driving electrodes even if the angle of field of display is changed. For this reason, the surface area of the black matrix can be minimized and correspondingly, the opening of the picture elements is relatively high.
However, this system in which the black matrix is directly formed on an active device (such as thin film transistor) a driving circuit by applying a pigment dispersion onto the surface of the circuit often suffers from a problem of faulty operations of thin film transistors (TFT) or thin film diodes (TFD, also called MIM) serving as driving elements for the liquid crystal display device.